The National Security Agency has sent spies into private companies in a bid to compromise networks from within, according to documents leaked by Edward Snowden.

Agents sent in by the NSA targeted global communications firms under a highly classified 'core secrets' program dubbed Sentry Eagle previously known only to a handful of officials. The documents indicate operatives in the core secrets program worked in concert with companies to weaken encryption and spent hundreds of millions of dollars to break security mechanisms. The document listed facts ranging from unclassified to top secret necessitating "extraordinary protection".